| The Basics The History The Genetic Path The Symptoms The Phenotypes The Treatments The Testing |
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Is alpha-1 antitrypsin deficiency inherited?
Alpha-1 antitrypsin deficiency is inherited in families in an autosomal codominant pattern. Codominant inheritance means that two different variants of the gene (alleles) may be expressed, and both versions contribute to the genetic trait. The M gene is the most common allele of the alpha-1 gene. It produces normal levels of the alpha-1 antitrypsin protein. The Z gene is the most common variant of the gene. It causes alpha-1 antitrypsin deficiency. The S allele is another, less common variant that causes ATTD. If a person inherits one M gene and one Z gene or one S gene ('type PiMZ' or 'type PiMS'), that person is a carrier of the disorder. While such a person may not have normal levels of alpha-1 antitrypsin, there should be enough to protect the lungs. However, carriers with the MZ alleles have an increased risk for lung disease, particularly if they smoke. A person who inherits the Z gene from each parent is called 'type PiZZ.' This person has very low alpha-1 antitrypsin levels, allowing elastase - an enzyme especially of pancreatic juice that digests elastin - to damage the lungs. A person who inherits an altered version called S and Z is also likely to develop AATD.
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This disorder is caused by a
mutation in the proteinase inhibitor (PI) gene on chromosome 14. The normal
protein coded for by this gene is involved in tissue repair. Disorder symptoms
depend on which type of mutation an individual has in the PI gene. There are
more than 70 different alleles of the PI gene.